This invention relates generally to the field of propulsion system aerodynamics and more specifically to a new and improved nacelle installation for front fan, gas turbine engines for aircraft propulsion.
The performance of new aircraft systems requires an increased emphasis on the installed performance of the propulsion system for providing a more fuel efficient and quieter aircraft. One significant consideration is the interaction between the aircraft and its propulsion system. Installation effects on the propulsion system were shown in the past to have been significant causes of aerodynamic performance losses.
One aircraft and engine interface performance loss area is the aircraft pylon and its attachment to the engine mounting system. In high speed aircraft and especially aircraft where the jet engine is installed relatively close to an aircraft structural member such as a wing, there tends to be interference in the flow of gas from the core exhaust nozzle of the engine with the adjacent aircraft structure. Furthermore, the development of advanced wing shapes and shorter and lighter propulsion systems has led to pylon-engine interface performance problems.
More specifically, for increasing aerodynamic efficiency, the desired mounting and placement of a wing mounted engine nacelle is below and partly forward of the wing and therefore requires highly swept, aerodynamically shaped pylon configurations. The combination of a highly swept pylon and a relatively short nacelle can result in hot exhaust gas upwash over the pylon trailing portion.
Furthermore, the undesirable interference known as base drag which is accompanied by a low pressure zone can exist between the engine and the aircraft. Hot exhaust gas upwash over and drag on the pylon can reduce aerodynamic performance and possibly adversely affect pylon panel structural integrity. More specifically, where the pylon skin or panel structure comprises fiberglass or the like, the hot exhaust gas upwash flowing over the fiberglass pylon panels can reduce the panel strength and lead to aerodynamically induced vibrations and fatigue thereof.